1. Field of the Invention
The present invention relates to a glow plug with a glow tube into which an inner pole projects and which is connected via heating and control spirals to the glow tube.
2. Description of Related Art
In conventional glow plugs, heating and measurement spirals are arranged in a series connection in succession, with the heating spiral being located in the forward area of the glow pin. The heating spiral is connected via a control spiral to the inside pole of the glow plug. The control spiral consists of a material which has a positive or a negative temperature coefficient of resistance, so that in this way self-regulation of the glow current for the heating element takes place, by which overheating of the heating element is avoided.
The control behavior of the control element is influenced, in addition to heating by the flowing current, by the heat radiation of the series-connected heating element. This heat passage from the heating spiral to the control spiral via a wire connection or via the spiral vicinity, however, requires a certain time and takes place nonuniformly from the direction of the heating spiral. This results in a delayed and nonuniform effect on the control behavior of the control spiral; this can lead to the heating spiral""s melting through.
A primary object of the present invention is to provide a glow plug in which the control spiral is influenced more uniformly and promptly by the temperature of the heating spiral, and thus controlled, and the heating spiral being made as a measurement spiral for control of supply of the glow current.
This object is achieved by locating the control spirals with respect to the heating spirals so that the control spirals are uniformly heated by the heating spirals over a majority of their length.